Electric hammer drills are required to provide a rotary drive for rotating the drill and a reciprocatory drive which is converted into a hammering action on the drill. The reciprocatory drive is obtained from a rotary crank-shaft and piston mechanism or other rotary shaft-driven mechanism. In the well-known type of electric hammer drill in which the motor is disposed with its output shaft at right angles to the drill axis, the motor is located adjacent the handle so as to achieve the best balance of the tool for the operator. In the most common constructions of this kind, of which U.S. Pat. No. 3,161,242 shows an example, an output pinion on the motor shaft meshes with a first gear on a parallel shaft which drives the reciprocatory mechanism and which has fixed to it a second gear forming part of a reduction gear for rotating the drill. The chief disadvantage of this arrangement is that any change in the reduction ratio of the drive from the motor shaft to the said parallel shaft to alter the hammering frequency also produces a change in the relationship between the motor speed and the drill speed. In a mechanism shown in U.S. Pat. No. 3,521,497, the two gears which respectively drive the reciprocating mechanism and rotate the drill engage the motor pinion at diametrically opposite sides thereof, so that the aforesaid disadvantage is overcome and the advantage of a lower tooth loading on the motor pinion is obtained. However, the general layout of the hammer drill dictates that the two said gears are respectively disposed at the handle side and drill side of the tool, and the motor must be positioned sufficiently far forward of the handle to allow for this, so that the resulting tool is less well balanced.